The present invention relates to an adjustable table which is tiltably positioned by adjusting elements over a fixed base, and particularly to an adjustable table for use with precision measuring devices.
It is a known practice from West German DE-AS No. 2,515,828, to support an adjustable table of the above-mentioned type by means of three spheres arranged to bear on a fixed base in a conical depression, a prismatic groove and a plane surface, respectively. By adjusting the last two spheres, which lie on oblique prisms of the adjustable table, the table can be swung in two vertical planes perpendicular to one another about the sphere arranged in the conical depression. This arrangement presents the disadvantage that the three support points differ in rigidity, that thermal expansion can cause decentering of the table, and that the point contacts between the balls and the prismatic groove and the plane surface are susceptible to wear and deformation.
When three spheres are mounted on the fixed base and are positioned in three prisms running radially with respect to the center of the adjustable table, substantially no decentering of the table results from temperature changes, but in this case friction at the resting points must be overcome. This friction may generate forces in the table which can affect its levelness. Furthermore, wear occurs at the point contacts between the spheres and the prisms, and this wear is increased when the table is adjusted by a grinding of the spheres into the prism surfaces, so that the spheres are no longer freely shiftable in the prisms and for that reason a statically determined rest position is no longer provided.
In West German DE-AS No. 2,248,535 there is described an adjustable table that includes three plates lying one upon another, which are slidable in the horizontal plane by means of spheres placed in prismatic guides via adjusting elements, and in the vertical plane are tiltably borne by means of further spheres which bear on plane surfaces and on slopes. This arrangement is also subject to wear at the point contacts between the spheres and the plane surfaces and the prisms.
From West German DE-OS No. 2,543,564 one learns of a table that is tiltably supported on a rigid intermediate body by means of obliquely disposed bearing elements, wherein the intermediate body is horizontally shiftable by means of roller bodies with respect to a base. In West German DE-OS No. 1,772,599 there is shown an adjusting arrangement having a row of plates disposed one over another. In each case two plate surfaces lying opposite one another are designed for straight-line flat horizontal displacement and, in each case, two oppositely lying surfaces are provided with a construction for swinging about a horizontal axis. These two arrangements present the disadvantage that the adjustable surface is decentered by the swinging movement, so that a subsequent centering must be performed.